D(-)-3-hydroxybutyrate and acetoacetate have been shown to be metabolites of consequence in the neonate during the myelination period. The experiments described in this proposal seek to establish the relative importance of the ketone bodies, D(-)-3-hydroxybutyrate and acetoacetate, and glucose for respiration and lipid synthesis in the developing rat during this period. It is proposed that lactate produced by active glycolysis in the central nervous system and possibly other organs is utilized by active gluconeogenesis in liver and kidney for the maintenance of glucose homeostasis. It is proposed that a glucose-lactate cycle exists during myelination in the neonatal rat. Studies to examine the interdependence of brain glucose and liver lactate metabolism during development are described. The effects of nutritional and metabolic perturbations on ketone body and glucose utilization for respiration and lipid synthesis in artificially reared rats will be examined. The role of L(plus)-3-hydroxybutyrate as a metabolite of consequence during development will be investigated. Many of the methods described in the proposal have been used successfully in our laboratory and will be extended by the studies in this project.